Semiconductor light emitting device and method for manufacturing the same

ABSTRACT

A semiconductor light emitting device includes a semiconductor light source, a resin package surrounding the semiconductor light source, and a lead fixed to the resin package. The lead is provided with a die bonding pad for bonding the semiconductor light source, and with an exposed surface opposite to the die bonding pad The exposed surface is surrounded by the resin package in the in-plane direction of the exposed surface.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a semiconductor light emitting deviceused as e.g. a light source of a cell phone or a pixel light source of ahigh-definition dot matrix display. The invention also relates to amethod for manufacturing such a semiconductor light emitting device.

2. Description of the Related Art

FIG. 13 illustrates an example of conventional semiconductor lightemitting device (see JP-A-2001-196641, for example). The semiconductorlight emitting device illustrated in the figure includes a substrate 91formed with a pair of electrodes 92A and 92B, and an LED chip 94 bondedto the substrate 91. The LED chip 94 and the bonding wire 96 are coveredwith a resin package 95. The electrode 92A is formed with a die bondingpad 92Aa. The LED chip 94 is bonded to the die bonding pad 92Aa using Agpaste 93. The electrode 92B is formed with a bonding pad 92Ba to whichthe bonding wire 96 is bonded.

In recent years, size reduction of e.g. a cell phone is stronglydemanded. Accordingly, there also exists a strong demand for sizereduction of a semiconductor light emitting device. In the conventionalsemiconductor light emitting device X, the enhancement of the brightnessof the LED chip 94 involves an increase in the current to flow throughthe LED chip 94, which increases the heat generated from the LED chip94. However, since the substrate 91 is generally made of a material suchas glass-fiber-reinforced epoxy resin, the thermal conductivity of thesubstrate 91 is relatively small. Thus, as to the conventionalsemiconductor light emitting device X, there is still room forimprovement for the efficient dissipation of heat from the LED chip 94and the size reduction of the device.

SUMMARY OF THE INVENTION

The present invention has been proposed under the circumstancesdescribed above. It is, therefore, an object of the present invention toprovide a semiconductor light emitting device which is capable ofachieving size reduction, efficient heat dissipation and highbrightness.

According to a first aspect of the present invention, there is provideda semiconductor light emitting device comprising: a semiconductor lightsource; a resin package surrounding the semiconductor light source; anda lead fixed to the resin package. The lead is provided with a diebonding pad for bonding the semiconductor light source, and with anexposed surface opposite to the die bonding pad and exposed to anoutside of the resin package. The exposed surface is surrounded by theresin package in the in-plane direction of the exposed surface.

With this arrangement, the heat from the semiconductor light sourceefficiently escapes through the lead. Further, the lead can have thesmallest size that allows proper mounting of the semiconductor lightsource. Thus, the size reduction and high brightness of thesemiconductor light emitting device can be achieved.

Preferably, the semiconductor light source may comprise a plurality ofsemiconductor light emitting elements bonded to the die bonding pad.

Preferably, the lead may be formed with a thin portion closer to thedie-bonding pad in the thickness direction of the lead.

According to a second aspect of the present invention, there is provideda semiconductor light emitting device comprising: a semiconductor lightsource; a resin package surrounding the semiconductor light source; andat least one lead fixed to the resin package. The lead includes a thinportion and a thick portion formed integral with the thin portion, wherethe thin portion and the thick portion include first surfaces flush witheach other and second surfaces opposite to the first surfaces. Thesecond surface of the thick portion is exposed to the outside of theresin package, while the second surface of the thin portion is coveredby the resin package.

Preferably, the semiconductor light source may be mounted on the firstsurface of the thin portion.

Preferably, the semiconductor light emitting device of the second aspectmay further comprise an additional lead spaced apart from theabove-mentioned one lead, where the additional lead comprises a thinportion and a thick portion formed integral with the thin portion. Theboundary between the thin portion and the thick portion of theabove-mentioned one lead and the boundary between the thin portion andthe thick portion of the additional lead are on the same straight line.

Preferably, the thick portion of the above-mentioned one lead may beformed with a projection extending perpendicularly to the thicknessdirection of the thick portion.

According to a third aspect of the present invention, there is provideda method for manufacturing a semiconductor light emitting device. Themethod comprises the following steps. First, a lead is formed bypressing a part of a metal plate, so that the resultant lead includes athin portion and a thick portion integral with the thin portion, wherethe thin and the thick portions share a flat first surface and havestepped second surfaces opposite to the first surface. Then, asemiconductor light emitting element is mounted on the first surfacementioned above, and a resin package for partially covering the lead isformed in a manner such that the second surface of the thick portion isexposed to the outside of the resin package, and the second surface ofthe thin portion is covered by the resin package.

Other features and advantages of the present invention will become moreapparent from detailed description given below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view illustrating a semiconductor light emittingdevice according to a first embodiment of the present invention;

FIG. 2 is a bottom plan view illustrating the semiconductor lightemitting device according to the first embodiment of the presentinvention;

FIG. 3 is a sectional view taken along lines III-III in FIG. 1 ;

FIG. 4 is a sectional view taken along lines IV-IV in FIG. 1 ;

FIG. 5 is a top plan view illustrating a semiconductor light emittingdevice according to a second embodiment of the present invention;

FIG. 6 is a bottom plan view illustrating the semiconductor lightemitting device according to the second embodiment of the presentinvention;

FIG. 7 is a top plan view illustrating a semiconductor light emittingdevice according to a third embodiment of the present invention;

FIG. 8 is a bottom plan view illustrating the semiconductor lightemitting device according to the third embodiment of the presentinvention;

FIG. 9 is a sectional view taken along lines IX-IX in FIG. 7 ;

FIG. 10A is a top plan view illustrating a step of the process formaking a thin portion;

FIG. 10B is a sectional view for illustrating the step depicted in FIG.10A;

FIG. 10C is a sectional view illustrating another step of the process;

FIG. 11 is a top plan view illustrating a semiconductor light emittingdevice according to a fourth embodiment of the present invention;

FIG. 12 is a sectional view taken along lines XII-XII in FIG. 11 ; and

FIG. 13 is a sectional view illustrating a conventional semiconductorlight emitting device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-4 illustrate a semiconductor light emitting device according toa first embodiment of the present invention. The semiconductor lightemitting device A1 of the first embodiment includes a lead 1A, aplurality of leads 1B, three LED chips 2, a resin package 4 and sealingresin 5. In FIG. 1 , the illustration of the sealing resin 5 is omittedfor convenience. The semiconductor light emitting device A1 is designedas a very small and thin semiconductor light emitting device having asize of about 3 mm×3 mm in plan view and a thickness of about 0.5 to 0.6mm.

The leads 1A and 1B serve to support the LED chips 2 and supply electricpower to the LED chips 2. For instance, the leads 1A and 1B are made ofCu, a Cu alloy or an Fe—Ni alloy and have a thickness of about 0.1 mm.The lead 1A includes a die bonding pad 11, an exposed surface 12 and athin edge portion 13. The die bonding pad 11 is generally in the form ofa strip. The LED chips 2 are bonded to the die bonding pad 11. Asillustrated in FIG. 2 , the exposed surface 12 is positioned on theopposite side of the die bonding pad 11 and exposed to the outside ofthe resin package 4. The four sides of the exposed surface 12 aresurrounded by the resin package 4. As illustrated in FIGS. 3 and 4 , thethin edge portion 13 surrounds the die bonding pad 11. The thin edgeportion 13 is flush with the die bonding pad 11 and is not exposed onthe exposed surface 12 side.

Each of the leads 1B includes a wire bonding pad 14, a terminal 15 and athin edge portion 16. A wire 3 is bonded to the wire bonding pad 14. Theterminal 15 is a surface on the opposite side of the wire bonding pad 14and exposed to the outside of the resin package 4, as illustrated inFIG. 2 . As illustrated in FIG. 3 , the thin edge portion 16 extendsfrom the wire bonding pad 14 and is not exposed on the terminal 15 side.

The LED chip 2 is the light source of the semiconductor light emittingdevice A1. For instance, the LED chip 2 has a laminated structure madeup of an n-type semiconductor layer, a p-type semiconductor layer and anactive layer sandwiched between these semiconductor layers. In thisembodiment, three LED chips 2 are mounted. For instance, the three LEDchips 2 emit red light, green light and blue light, respectively.

The resin package 4 is made of e.g. white resin and partially coverseach of the leads 1A, 1B. The resin package 4 includes an inwardlyinclined surface 4 a surrounding the three LED chips 2. The inwardlyinclined surface 4 a functions as a reflector for reflecting the lightemitted laterally from the LED chips 2 toward the outside of thesemiconductor light emitting device A1. For instance, the resin package4 is molded as one piece by injecting molten resin into a mold in whichthe leads 1A and 1B are set.

The sealing resin 5 protects the LED chips 2 and the wires 3. Thesealing resin 5 is loaded to fill the space surrounded by the inwardlyinclined surface 4 a. The sealing resin 5 is made of e.g. an epoxy resinpermeable to the light emitted from the LED chips 2.

The advantages of the semiconductor light emitting device A1 will bedescribed below.

According to the first embodiment, the heat from the LED chips 2efficiently escapes through the exposed surface 12 to e.g. a circuitboard on which the semiconductor light emitting device A1 is mounted.This makes it possible to increase the brightness of the semiconductorlight emitting device A1.

Further, the lead 1A is surrounded by the resin package 4 from the foursides and does not extend to reach the edge of the resin package 4.Herein, to increase the brightness, it is desirable to arrange the LEDchips 2 at the center of the semiconductor light emitting device A1.Thus, with the arrangement of the first embodiment, the lead 1A can havethe smallest possible size which allows the proper mounting of the LEDchips 2. This is desirable for the size reduction of the semiconductorlight emitting device A1.

By mounting the three LED chips 2 on the die bonding pad 11, the LEDchips 2 are arranged close to each other. This is suitable for promotingthe mixing of light emitted from the three LED chips 2.

The provision of the thin edge portions 13 and 16 prevents the leads 1Aand 1B from dropping from the resin package 4.

FIGS. 5 and 6 illustrate a semiconductor light emitting device accordingto a second embodiment of the present invention. The semiconductor lightemitting device A2 of the second embodiment differs from that of thefirst embodiment in shape of the die bonding pad 11 (lead 1A). In thesefigures, the elements which are identical or similar to those of thefirst embodiment are designated by the same reference signs as thoseused for the first embodiment.

As illustrated in FIG. 5 , in the second embodiment, the width of thedie bonding pad 11 changes stepwise in the longitudinal direction.Specifically, the die bonding pad 11 includes a relatively wide portion17 on which two LED chips 2 are bonded and a relatively narrow portion18 on which one LED chip 2 is bonded. In this embodiment, the three LEDchips 2 can be arranged at the vertices of a triangle. This arrangementis desirable for the mixing of light emitted from the three LED chips 2.

FIGS. 7-9 illustrate a semiconductor light emitting device according toa third embodiment of the present invention. In these figures, theelements which are identical or similar to those of the foregoingembodiments are designated by the same reference signs as those used forthe foregoing embodiments. In the third embodiment, the horizontaldirection in FIG. 7 is defined as the X direction, whereas the directionperpendicular to the X direction is defined as the Y direction.

As noted before, each of the semiconductor light emitting devices A1 andA2 of the first and the second embodiments includes a single lead 1A anda plurality of leads 1B. Unlike this, the semiconductor light emittingdevice A3 of the third embodiment includes a plurality of pairs of leads1A and 1B. Specifically, as illustrated in FIG. 7 , three leads 1A andthree leads 1B are arranged to be spaced from each other in the Ydirection to make three pairs of leads 1A and 1B spaced from each otherin the X direction.

As illustrated in FIG. 9 , each of the leads 1A and 1B is in the form ofa plate comprising a thick portion 21 having a relatively largethickness and a thin portion 22 having a relatively small thicknesswhich are connected to each other in the Y direction. The thin portion22 has an upper surface 22 a which is flush with the upper surface ofthe thick portion 21 and a retreated lower surface 22 b. The thickportion 21 has a lower surface 21 b exposed to the outside of the resinpackage 4. The lower surface 21 b serves as a terminal for mounting thesemiconductor light emitting device A3 onto a non-illustrated circuitboard. The lower surface 22 b of the thin portion 22 is covered with theresin package 4. The thick portion 21 has a thickness of about 0.15 mm,whereas the thin portion 22 has a thickness of about 0.1 mm.

As illustrated in FIG. 7 , the boundary between the thick portion 21 andthe thin portion 22 of each lead 1A is positioned on the straight lineL1 extending in the X direction. The boundary between the thick portion21 and the thin portion 22 of each lead 1B is positioned on the straightline L2 extending in the X direction. The leads 1A and 1B including thethin portions 22 can be formed by e.g. press working.

The process for making a thin portion 22 will be described below withreference to FIGS. 10A-10C. First, as illustrated in FIGS. 10A and 10B,metal plates 1A′ and 1B′ of a uniform thickness are set between a moldmember 23A for backup and a mold member 23B for pressing. The pressingportion of the mold member 23B is rectangular in plan, as seen from FIG.10A. Though not depicted, the metal plates 1A′ and 1B′ are integrallyconnected to each other via e.g. a lead frame. Then, as illustrated inFIG. 10C, the mold member 23B is lowered to press predetermined parts ofthe respective metal plates 1A′ and 1B′. In each of the metal plates 1A′and 1B, the pressed part is formed into a thin portion 22. In this way,the leads 1A and 1B including thin portions 22 are made collectively byperforming a single pressing step with respect to the metal plates 1A′and 1B′. In the leads 1A and 1B, the boundary between the thin portion11 and the thick portion 12 corresponds to the edge of the moldingmember 23B.

The three LED chips 2 in the third embodiment may include LED chips 2R,2G and 2B for emitting red light, green light and blue light,respectively. As illustrated in FIG. 9 , the LED chips 2 are mountedindividually on the upper surfaces 22 a of the thin portions 22 of theleads 1A, 1B. A wire 3 is bonded, at one end, to each of the LED chips2. The other end of each wire 3 is bonded to the lead 1B (1A) which ispaired, in the Y direction, with the lead 1A (1B) on which the LED chip2 is mounted.

In the third embodiment, the LED chip 2R has a double-sided electrodestructure in which a pair of electrodes are formed on the two mainsurfaces. The LED chip 2R is bonded to the lead 1B located in the middlein the X direction. The LED chips 2G and 2B has a single-sided electrodestructure in which a pair of electrodes are collectively formed on onemain surface. The LED chips 2G and 2B are bonded to the leads 1A locatedon the two sides in the X direction. Two zener diodes 24 connected inparallel to be in reverse bias from the LED chips 2G, 2B are mounted onthe leads 1B located on the two sides in the X direction. With thisarrangement, excessive current is prevented from flowing through the LEDchips 2G and 2B.

The advantages of the semiconductor light emitting device A3 will bedescribed below.

According to the third embodiment, the heat generated from the LED chips2 efficiently escapes through the exposed surfaces of the leads 1A and1B (the lower surfaces 21 b of the thick portions 21) to e.g. a circuitboard on which the semiconductor light emitting device A3 is mounted.Further, as noted before, the leads 1A and 1B include thin portions 22,and the lower surfaces 22 b of the thin portions 22 are covered with theresin package 4. With this arrangement, even when the entire thicknessof the leads 1A and 1B is reduced to reduce the size of thesemiconductor light emitting device A3, the leads 1A and 1B do not dropfrom the resin package 4, because the thin portions 22 engage the resinpackage 4. Thus, the size reduction (thickness reduction) of thesemiconductor light emitting device A3 is achieved.

In the third embodiment, the thin portions 22 of the leads 1A and 1B areformed collectively by pressing using a rectangular mold member 23B.Thus, the thin portions 22 are formed easily, and the dimension of thethin portion 22 does not vary. This is desirable for reducing the sizeof the semiconductor light emitting device A3.

FIGS. 11 and 12 illustrate a semiconductor light emitting deviceaccording to a fourth embodiment of the present invention. Thesemiconductor light emitting device A4 of the fourth embodiment differsfrom the semiconductor light emitting device A3 of the third embodimentin that the leads 1A and 1B are formed with projections 31. In thesefigures, the elements which are identical or similar to those of theforegoing embodiments are designated by the same reference signs asthose used for the foregoing embodiments.

As illustrated in FIG. 11 , in the fourth embodiment, the thick portion21 of each lead 1A, 1B is formed with a plurality of projections 31projecting in a direction perpendicular to the thickness direction ofthe thick portion 21 at the surface contacting the resin package 4. Eachof the projections 31 is generally rectangular in plan view. Each of theprojections 31 is equal in thickness to the thin portion 12 and is notexposed at the reverse surface of the semiconductor light emittingdevice A4.

According to the fourth embodiment, the provision of the projections 31at the thick portions 21 of the leads 1A and 1B substantially increasesthe surface area of the leads 1A and 1B. As a result, the contact areabetween the leads 1A, 1B and the resin package 4 increases, whichachieves reliable adhesion of the leads 1A, 1B to the resin package 4.This arrangement more effectively prevents the leads 1A and 1B fromdropping from the resin package 4.

As another technique to enhance the adhesion of the leads 1A, 1B to theresin package 4, when the leads 1A and 1B are made of a material otherthan Cu, the surfaces of the leads 1A and 1B may be plated with Cu,which has a high affinity for the resin package 4, except the portionsto which the LED chips or wires are to be bonded. As still anothertechnique, shot blasting may be performed with respect to the surfacesof the leads 1A and 1B except the portions to which the LED chips orwires are to be bonded to form minute projections and recesses at thesurfaces. These techniques may be employed in combination as required.

The semiconductor light emitting device of the present invention is notlimited to the foregoing embodiments. The specific structure of thesemiconductor light emitting device according to the present inventionmay be varied in design in many ways.

For instance, the semiconductor light emitting device of the presentinvention does not necessarily need to include three LED chips foremitting red light, green light and blue light. The semiconductor lightemitting device may include an LED chip for emitting blue light and asealing resin in which a fluorescent material is mixed. In this case,the semiconductor light emitting device emits white light.Alternatively, the semiconductor light emitting device may include threeLED chips for emitting light of the same color (e.g. blue light). Whenthe LED chips emit light of the same color, the brightness of thesemiconductor light emitting device is enhanced.

In the third embodiment, the LED chips 2 are mounted on the thin portion22 of the leads 1A and 1B. Alternatively, the LED chips 2 may be mountedon both the thin portion 22 and the thick portion 21, or on the thickportion 21 only.

The invention claimed is:
 1. A light-emitting device comprising: first,second and third conductors disposed on a common plane and spaced apartfrom each other; a first protection element mounted on the firstconductor; a second protection element mounted on the second conductor;a first light-emitting element mounted on the third conductor; and aresin member supporting the first, second and third conductors, thefirst light-emitting element, the first protection element and thesecond protection element, wherein as viewed in a first directionparallel to the common plane, the first light-emitting element isdisposed between the first protection element and the second protectionelement.
 2. The light-emitting device according to claim 1, wherein asviewed in a second direction parallel to the common plane andperpendicular to the first direction, the first light-emitting elementis offset in the first direction with respect to the first protectionelement and the second protection element.
 3. The light-emitting deviceaccording to claim 2, further comprising a fourth conductor and a secondlight-emitting element mounted on the fourth conductor.
 4. Thelight-emitting device according to claim 3, further comprising a fifthconductor and a third light-emitting element mounted on the fifthconductor.
 5. The light-emitting device according to claim 4, whereinthe fifth conductor comprises a first portion extending in the firstdirection and a second portion extending in the second direction, andthe third light-emitting element is mounted on the second portion of thefifth conductor.
 6. The light-emitting device according to claim 4,wherein each of the first through the fifth conductor comprises aportion exposed from a bottom surface of the resin member.
 7. Thelight-emitting device according to claim 4, wherein the resin membercomprises a first edge and a second edge that are spaced apart from eachother in the first direction as viewed in a direction perpendicular tothe common plane, the first through the third conductors protrudeoutwards from the first edge of the resin member, and the fourth and thefifth conductors protrude outwards from the second edge of the resinmember.
 8. The light-emitting device according to claim 4, wherein thesecond light-emitting element and the third light-emitting elementoverlap with each other as viewed in the second direction.
 9. Thelight-emitting device according to claim 4, further comprising areflector formed on the first through the fifth conductors, wherein thereflector surrounds the three light-emitting elements and the twoprotection elements as viewed in a direction perpendicular to the commonplane.
 10. The light-emitting device according to claim 4, furthercomprising a sixth conductor disposed between the fourth conductor andthe fifth conductor, wherein the sixth conductor is connected to thefirst light-emitting element.
 11. The light-emitting device according toclaim 3, wherein the fourth conductor comprises a first portionextending in the first direction and a second portion extending in thesecond direction, and the second light-emitting element is mounted onthe second portion.
 12. The light-emitting device according to claim 11,further comprising first, second, third and fourth wires, wherein thefirst wire connects the first protection element to the fourthconductor, the second wire connects the second protection element to thefifth conductor, the third wire connects the second light-emittingelement to the first conductor, and the fourth wire connects the thirdlight-emitting element to the second conductor.
 13. The light-emittingdevice according to claim 12, wherein the first and the second wires aregreater in length than each of the third and the fourth wires.
 14. Thelight-emitting device according to claim 12, further comprising fifthand sixth wires, wherein the fifth wire connects the secondlight-emitting element to the fourth conductor, and the sixth wireconnects the third light-emitting element to the fifth conductor. 15.The light-emitting device according to claim 14, wherein the fifth wireis greater in length than the third wire, and the sixth wire is greaterin length than the fourth wire.
 16. The light-emitting device accordingto claim 14, wherein the fifth wire comprises an end attached to thefirst portion of the fourth conductor.
 17. The light-emitting deviceaccording to claim 14, wherein the fifth wire comprises an intermediateportion that does not overlap with the fourth conductor as viewed in adirection perpendicular to the common plane.
 18. The light-emittingdevice according to claim 11, wherein the second portion of the fourthconductor is greater in length than the second light-emitting element.19. The light-emitting device according to claim 2, wherein the firstprotection element and the second protection element overlap with eachother as viewed in the second direction.
 20. The light-emitting deviceaccording to claim 1, wherein the third conductor is disposed betweenthe first conductor and the second conductor.